Annual Research & Review in Biology

Background: Long-term internal exposure to trace environmental radionuclides poses significant health risks. This is especially true for those emitting high linear energy transfer (LET) alpha particles. Traditional radiotoxicology assessments rely heavily on in vitrocultures, mammalian models, or external irradiation systems. A critical research gap exists for chronic internal exposure models of low-penetrating alpha radiation. Such models must use biological uptake pathways to ensure accurate microdosimetry.

Aims: We aimed to evaluate the biological effects of chronic internal exposure to alpha radiation. To achieve this, we established a chronic ingestion and injury model in Caenorhabditis elegans (C. elegans). We used americium trichloride (AmCl₃) as the radiation source.

Methodology: We created an ingestion pathway using a liquid exposure system with inactivated Escherichia coli (E. coli) OP50 and neutralized AmCl₃ (pH 7.0). Age-synchronized L4 nematodes were continuously cultured for 1 to 3 days in a neutral environment. The single-well exposure dose was tightly controlled at 0.748 microsieverts (μSv). We quantified oxidative stress, neurally regulated chemotaxis, and reproductive toxicity. This was achieved using behavioral assays and transgenic fluorescent reporter strains (CF1553, CL2166, PD4251, RW1596).

Results: We discovered highly tissue-specific damage under this extremely low-dose exposure. The expression of antioxidant genes (sod-3 and gst-4) showed a time-dependent, biphasic fluctuation. This process included stress activation, compensatory adaptation, and eventual decompensation. Conversely, body wall muscle structure and chemotaxis function remained normal. This indicates robust radioresistance in these highly differentiated tissues. Our key finding is the pronounced radiosensitivity of the reproductive system. While the basal brood size remained unaffected, the embryo hatching rate decreased significantly (p < 0.001). This was accompanied by localized protruding vulva malformations.

Conclusion: This in vivo ingestion-based model effectively reveals the damage induced by endogenous alpha emitters. The observed damage is both time-dependent and tissue-specific. This framework provides a robust biological platform. It can elucidate the toxicological mechanisms of internal radiation and help screen potential radioprotective interventions.